A vibration wave motor serving as an example of a vibration type actuator is a non-electromagnetic driving type motor configured to generate, by applying an alternating voltage to an electro-mechanical energy conversion element such as a piezoelectric element coupled to an elastic member, high-frequency vibration in the piezoelectric element, and to output the generated vibration energy as a continuous mechanical motion.
A vibration type driving apparatus including a vibration type motor is used for automatic focus driving of a camera, for example. Highly-precise positioning con required for the automatic focus driving, so position feedback control using a position sensor is performed. A speed of the vibration type motor can be controlled by adjusting a frequency or a drive pulse width of a driving signal applied to a piezoelectric element, a phase difference between two driving signals, or the like. For example, the closer a driving frequency comes to a resonance frequency of the piezoelectric element, the larger vibration amplitude becomes. Thus, a lens serving as a driving target can be driven at high speed.
In recent years, there have been increasing needs for driving a heavier target at higher speed. As one technical solution thereof, a vibration type motor using a plurality of vibrators has been proposed. An issue in the vibration type motor using the plurality of vibrators lies in that the vibrators differ from each other in speed because they differ in resonance frequency due to individual variation. To correct the speed difference, a driving circuit may be individually provided to adjust a driving frequency for each of the vibrators. However, the cost of the driving circuit increases. Therefore, in order to drive the plurality of vibrators at the same speed using a common driving circuit, the driving circuit needs to be devised in some way.
PTL 1 discusses a driving circuit that drives a plurality of vibration type motors with the same rotation number by one transformer boosting circuit. To make the rotation number uniform, the technique discussed therein adjusts a driving voltage applied to each of the vibration type motors, using capacitance division of a capacitor.
PTL 2 similarly discusses driving a plurality of vibrators by one transformer driving circuit. For the purpose of performing impedance matching for vibrators having different resonance frequencies by one transformer boosting circuit, different reactance elements are respectively connected to the vibrators. An electric resonance frequency can be adjusted according to each of the vibrators. Thus, a circuit constant of a transformer can be used without being changed.